A C-25 highly branched isoprenoid alkene and C-25 and C-27 n-polyenes in the marine diatom Rhizosolenia setigera

A North Atlantic strain of the marine diatom Rhizosolenia setigera was exam ined for the presence of hydrocarbons. This strain biosynthesizes a highly branched isoprenoid (HBI) C-25 pentaene, in contrast to Australian strains of R. setigera which produce HBI C-30 alkenes. The more widespread occurren ce of C-25 HBI alkenes compared to their C-30 counterparts in sea water and sediments may reflect the fact that C-25 HBI alkenes occur both in Haslea and R. setigera. The North Atlantic R, setigera strain also biosynthesizes C-25 and C-27 n-polyenes with six or seven double bonds in relatively high amounts. Their carbon number distribution was found to depend on growth tem perature. These lipids may be the precursors for C-25 and C-27 2-n-alkylthi ophenes, which are important organosulfur compounds in sediments from palae o upwelling regions. The distribution of these thiophenes may have potentia l for reconstruction of palaeo sea surface temperatures. (C) 1999 Elsevier Science Ltd. All rights reserved.